The invention relates to pulse width detectors and more particularly to apparatus and methods for measuring pulse widths in semiconductor circuits during the manufacture thereof.
As is known in the art, in the manufacture of semiconductor circuits, a significant cost is incurred in testing such circuits. Testing is necessary to detect manufacturing or design defects effecting operational characteristics of the circuits. For example, many semiconductor circuits, such as Dynamic Random Access Memories (DRAMs), use internally-generated pulses to convey information. Different pulse widths (i.e., time durations) convey different information. Because the pulses can control various functions of the circuit, it is desirable to test the circuit to ensure that all of the pulses produced by the circuit have proper pulse widths.
Much of the cost for testing these circuits is the result of the cost of the test equipment. With pulse widths typically on the order of 2-4 ns, the test equipment needs to have a very fine time resolution in order to determine whether the pulse has an acceptable pulse width. If the pulse width is measured by probing a conductor carrying the pulse and the test equipment used to sample the pulse on the conductor, then the test equipment needs to sample the pulse at a frequency on the order of 1 GHz (i.e., a sampling period of 1/10.sup.9 seconds or 1 nanosecond (ns)) in order to provide a time duration resolution on the order of 1 ns. Test equipment having operational or sampling frequencies this high is typically very expensive.